Why so many carbs?

[flyingace]

I think it has to do with engine design. An inline 4-cylinder motorcycle spins fast and makes its power at high rpms. A single carb with an intake manifold would not allow the engine to breath as fast at higher RPM. Not only that, but I think the long carb to cylinder distance would have an effect on throttle response, especially for the two outside cylinders. In cars, this is countered with big flywheels - something M/Cs don't want.

I'm no engineer, so this is all semi-educated guesses.

[t3rmin]

I think it has to do with engine design. An inline 4-cylinder motorcycle spins fast and makes its power at high rpms. A single carb with an intake manifold would not allow the engine to breath as fast at higher RPM.

Well I suppose it all depends on size. A single carb with the same CFM rating as the combined capacity of multiple carbs should breathe just as much. But there may be a point at which it's not practical or possible to make a carb big enough to meet the requirements of a motor. Although I can't see that happening in the context of a small motorcycle engine. A single Holley double pumper can easily meet the requirements of a big block V8...

Not only that, but I think the long carb to cylinder distance would have an effect on throttle response, especially for the two outside cylinders. In cars, this is countered with big flywheels - something M/Cs don't want.

Yeah, I think carb to cylinder distance would have some effect on throttle response. Though you probably have quite a bit of leeway before it becomes a problem (again, consider high-rise air-gap intakes and tunnel rams on muscle cars). AFAIK the varying distance between the outside and inside cylinders is usually accounted for by way of putting extra twisties in the inside intake runners, so they all end up being the same length, which would be just as possible on a motorcycle.

[flyingace]

I guarantee you if they could have figured out a way to put a carb on each cylinder of a muscle car, they would have. It would have kicked the living daylights out of anything with a manifold. Breathing isn't just about CFM, it's about efficiency as well. A direct path into the cylinder will always mean better breathing than going around corners.

[t3rmin]

They did/do put multi-carbs on cars (like this), and I think it is more efficient for the same reason we've figured out in this thread: more even mixture to all cylinders. All I'm saying is I don't think it's for capacity or carb-cylinder distance reasons.

[flyingace]

Where is Kevin Cameron when you need him?

[Arkaloid]

......because multi-point injection is better than throttle-body injection (or so I assume, since that's the modern FI incarnation). ;-)

throttle body F.I. is really no better than a precisely engineered carb setup. it was a cheap alternative for F.I. that detroit used to save on costs.

[Pete Logan]

You also must keep in mind that any manifold is a compromise. fuel distribution will not be equal across all cylinders with a one-carbed/manifold setup.

Now there ya go talking sense again - what have I told you about that

Get on the page girls. It's obvious that each cylinder should have it's own carb and it's own exhaust.

The only way to deliver the same charge to each cylinder is to have it's own carb with the exact same entry path as every other cylinder, and the only reason manifolds were invented was to save money on carbs, which are a bloody sight more expensive than manifolds.

Which is why manifold EFI is a bust and the only way EFI is gonna beat carbs is by direct injection.

Which is what a multi-carb setup did in the first place, only cheaper.

God, I'm good when I'm drunk

[Pete Logan]

throttle body F.I. is really no better than a precisely engineered carb setup. it was a cheap alternative for F.I. that detroit used to save on costs.

\\/ \\/ \\/

[t3rmin]

throttle body F.I. is really no better than a precisely engineered carb setup. it was a cheap alternative for F.I. that detroit used to save on costs.

Well I suppose precisely engineered is the key phrase there! But it's still going to be slightly more precise, with infinitely-adjustable computer control rather than a finite number of circuits (idle, off-idle, mains, power valve, etc.), plus (as I just read on Wikipedia) FI atomizes the fuel better. Then there's the maintenance-free aspect...

I see what you're saying, though. Throttle body FI is basically the same thing as a carburetor.

Not that I'm crazy about FI. I'd rather ream out a clogged jet than mess with a tangle of wires any day!

[Pete Logan]

I see what you're saying, though. Throttle body FI is basically the same thing as a carburetor.

Almost.

Throttle body FI is almost the same thing as carb through a manifold.

Direct injection FI is almost the same thing as one carb per cylinder.

Throttle body FI can be better than manifold carbs, but never as good as one carb per cylinder.

Direct injection FI can be better than that, but only with a good ECU and a better tuner.

Fun round here,ain't it

[t3rmin]

Well.... that's what I meant. ;-)

[ghwrenchit]

Maybe we need to toss timing and firing order into the mix, for a thought. For HP and good fuel economy, intake runner and exhaust length per cylinder is critical from what I know (little ).

On old big block tunnel ram intakes, nobody really cared if you got 8 miles to the gallon, just dump it in and go.

On small block's with good throttle response in every range, tuned (balanced) intake runner's and tuned headers (all pipes same length) were the way to go.

Old 6-pak setups 3x2bbl on 340's, common on Chrysler products in the late 60's early 70's were designed as progressive carb's, as they didn't all open equally at once but in series.

Newer hypo cars with fuel injection still balance the intake air runners and exhaust for length to each cylinder.

Perhaps on a bike, the realestate for a balanced intake/timing was not in the picture.

Dunno, just guess'in

ghwrenchit

[t3rmin]

I'm just bitter because I found gas in my oil and now I've got to go over the carbs. ;-)

[Tnutz]

carbs are ****....i hate them in every way. Too lean, to rich, runs but won't idle blah blah blah....my buddy's victory is EFI and all it does is start....no ****ing around....all he had to do was get a ecu flash for his pipes and it runs like a dream...No parts to wear out like a carb, no synching...maybe a clogged injector someday....but thats about it....:-D technology! once you go efi you will never go back.

[ghwrenchit]

carbs are ****....i hate them in every way. Too lean, to rich, runs but won't idle blah blah blah....my buddy's victory is EFI and all it does is start....no ****ing around....all he had to do was get a ecu flash for his pipes and it runs like a dream...No parts to wear out like a carb, no synching...maybe a clogged injector someday....but thats about it....:-D technology! once you go efi you will never go back.

..... I'm just bitter because I found gas in my oil and now I've got to go over the carbs.

All part of the "hobby"..... think the guy crank starting the model T wished he had a electric starter??? Be proud, fix, and ride!!!! :-D :-D

G